Non-selective Effects of Amiloride and Its Analogues on Ion Transport Systems and Their Cytotoxicities in Cardiac Myocytes

Abstract

The effects of amiloride and its analogues (3'', 4''-dichlorobenzamil (DCB), 2'', 4''-dimethylbenzamil (DMB), 5-(N-ethyl-N-isopropyl)amiloride (EIPA) and 5-(N-methyl-N-isobutyl)amiloride (MIBA)) on cardiac ion transporters (Na⁺/Ca²⁺ exchanger, Na⁺/H⁺ exchanger, Na⁺ pump and Ca²⁺ pump) and their cytotoxicities were tested in cardiac myocytes. All the tested compounds showed concentration-dependent inhibitory effects on the ion transporters studied in canine cardiac sarcolemmal vesicles. The concentrations (μM) of amiloride, DCB, DMB, EIPA and MIBA required to produce 50% inhibition were > 1000, 19, 10, 83 and 84, respectively, for the Na⁺/Ca²⁺ exchanger; 130, 73, 63, 16 and 14 for the Na⁺/H⁺ exchanger; > 1000, 72, > 300, > 300 and > 300 for the Na⁺ pump; and > 1000, 37, 93, 90 and 70 for the Ca²⁺ pump, respectively. Furthermore, these agents induced cell death in isolated rat cardiac myocytes and the 50% lethal concentrations (μM) were > 1000, 9.2, 30, 16 and 17, respectively. These findings demonstrate that amiloride and its analogues have non-selective inhibitory effects on cardiac ion transporters and cytotoxicity in cardiomyocytes. When these drugs are employed as experimental tools to investigate the involvement of ion transporters in cell functions, the results must be interpreted with caution.